(a) Field of the Invention
The present invention relates to an optical network unit and a method for controlling the unit in a hybrid passive optical network system.
(b) Description of the Related Art
With the development of optical communication technologies and a rapid increase in the demand on Internet services, fundamental researches on optical network have been conducted since the early 2000s. As a result, broadband networks, such as Fiber To The Home (FTTH) and Fiber To The Office (FTTO), have emerged and become common, in which the broadband network directly connects a base station or a central office (CO) to a subscriber using optical fibers.
Additionally, numerous researches have been recently conducted on technologies of the next generation high-speed and high-capacity optical network to cope with an explosive increase in traffic according to proliferation of mobile IP terminals, such as a smart phone or a table computer, commercialization of IPTV services, and proliferation of multimedia broadcasting/streaming services over the Internet.
As a method for efficiently providing services to more subscribers with a limited network resource, a time division multiplexing (TDM) technique and a wavelength division multiplexing (WDM) techniques have been applied to an optical subscriber network technology. In addition, many researches have been conducted on an optical network using a hybrid method to which the TDM method and the WDM method are applied together.
A hybrid type optical subscriber technology using both the TDM technique and the WDM technique are applied may meet the demand for a continued bandwidth expansion of a network and facilitate an expansion of communication capacity and the number of subscribers while providing ultra high speed communication services to more subscribers.
In international telecommunications union telecommunication (ITU-T) that is a main internal standardization organization, as a main technology of 40-gigabit-capable passive optical networks that is a 40G optical subscriber network technology, a PON technology and a point-to-point WDM technology of a time and wavelength division multiplexing scheme are selected and a standardization operation thereof has been progressed.
Like a time and wavelength division multiplexing passive optical network (TWDM-PON) system, a hybrid PON system in which various kinds of multiplexing techniques are mixed needs to be subjected to maintenance more than the existing PON system. For example, in the case of the TDM-PON system, to figure out and prevent a malfunction of optical network units (ONU), it is enough to observe a time, that is, a transmission time of allocated uplink signals in the viewpoint that each ONU observes a transmission time of an allocated uplink signal. On the other hand, in the TWDM-PON system, the TDM technique and the WDM technique are mixed, and therefore there is a need to prevent or stop the malfunction of the ONUs by figuring out the malfunction of the ONUs in consideration of the viewpoint of the time and the wavelength, in particular, the viewpoint that each ONU observes the wavelength of the allocated uplink signals. Transmitting, by a specific ONU, the uplink signal at different wavelengths from the allocated wavelength may have an adverse effect on the whole system.
In particular, the TWDM-PON system may use an ONU including a wavelength tunable light source, may not fix uplink/downlink transmitting/receiving wavelengths but change the uplink/downlink transmitting/receiving wavelengths of the ONU if necessary to balance a bandwidth load between channels, or when a total bandwidth consumption of a network is small, change some of channels to a power saving mode, and change the wavelength of the corresponding ONUs to a wavelength of different channels. Further, when abnormality of an optical distributed network (ODN) occurs, it is possible to change use wavelengths of the ONUs for protection switching. As such, when the wavelength various light source is used as an optical transmitter of the ONU, the wavelength setting malfunction occurs and thus an uplink optical signal may be output at a wavelength different from the allocated wavelength, such that the uplink transmission of other ONUs normally operated may have a disorder. Therefore, the hybrid PON system such as the TWDM-PON needs a wavelength setting monitoring function and a wavelength setting malfunction prevention function of the ONU having the wavelength tunable light source for a stable operation of the network
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.